Although not restricted to vehicles of the straddle carrier type, the invention will be described more specifically with reference to the tires with which these vehicles are equipped, as they have their own peculiar conditions of use. This type of vehicle is fitted with eight independent wheels which are mounted and set up independently, often causing the tires to drift sideways while the vehicle is in use.
The use of this type of vehicle is associated with shifting goods containers in ports. This use therefore corresponds to the shifting of heavy loads at low speeds usually of the order of 20 km/h.
The weight of the loads carried by this type of vehicle has led tire designers to develop special products which in particular have a relatively thick tread. This feature in particular avoids excessively rapid wear resulting from the loads being transported. Again on account of the weight of the loads being transported, the transverse grooves on the surface of the tread which is intended to come into contact with the ground have been abandoned in favor of circumferential grooves, particularly to avoid “saw-tooth” wear. Tires intended for this type of vehicle generally have two circumferential grooves dividing the tire tread into three circumferential regions or “ribs”.
The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the direction in which the tire rolls.
The transverse or axial direction of the tire is parallel to the axis about which the tire turns.
The radial direction is the direction that intersects the axis of rotation of the tire and is perpendicular thereto.
The axis of rotation of the tire is the axis about which it turns during normal use.
A radial or meridian plane is a plane containing the axis of rotation of the tire.
The circumferential mid-plane or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which splits the tire into two halves.
Because current user demand is towards increasingly heavy loads being transported at ever higher speeds, it has been found that the tires may degrade under certain conditions of use. In particular, the tread may begin to delaminate when the loads being transported become excessive and are carried around at high speeds.
Phenomena such as this can be explained in particular as a result of the substantial thickness of the tread which causes the rubber masses to heat up a great deal as a result in particular of the phenomena of the tire flattening in the contact patch that is in contact with the ground and as a result of friction against the ground. Such heating leads to risks of break up, this phenomenon in particular being dependent on the load being transported and on the speeds at which the tires are being used.